In our daily life, the role of optical fiber technology is getting more and more important. The sensitivity, stability and reproducibility of fiber components are more important when they are applied in the navigation, orientation and platform stability technologies. Because the manufacture process of fiber components (e.g. fiber coil) causes fiber's optical property change and loss, it will make the function of fiber components reduce and degrade.
In the prior art, several different strategies (US 2003/0007751A1 US 2005/0226563A1) are used to solve the problem in optical property change or loss in optical fiber elements. For example, the polarization-maintaining (PM) fiber can be applied to keep the polarization state of light, but the cost of PM fiber is high. Furthermore, the PM fiber ring around the coil is required to maintain the polarization extinction ratio, and this parameter is not easy to maintain. Thus it will increase the cost and difficulty in the manufacture process. Also, the quality of fiber coil is easily affected easily by fiber quality, stress and strain in the winding process, and the rubber filled in the fiber coil. As a result, every fiber coil may produce different levels of optical properties such as linear birefringence (LB), linear diattenuation (LD) and circular birefringence (CB) characteristics or their combination.
For a long time, the high-quality fiber coil winding process in fiber gyroscopes is a high-tech process. It requires not only the combination of special optical fiber and automatic tension control machines, but also the machine under a highly experienced mechanic operation in order to control the quality of fiber coil in an acceptable rage. Thus the high-tech process in fiber coil causes the production costs extremely high. If the quality of fiber coil (from different production dates or different plants) is uncontrollable, the fiber coil winding process needs additional time-consuming tests by re-adjusting fiber coil within the scope of the best quality. If you bypass this adjusting in fiber coil, the poor fiber coils are forced to the lower level in business. Thus the yield of high-quality fiber coil will be substantially reduced.
According to the present invention, applicants have departed from the conventional wisdom, and had conceived and implemented the free space single-mode fibers for fiber sensor, which is relative to that of compensating the fiber or fiber component such that the fiber or fiber component plus the compensated optical circuit act as if an Unitary Matrix free space condition. The disclosed free space single-mode fiber invention not only greatly enhances repeatability in the fiber and fiber component production line, it also can be employed to accelerate the design simulation for optical circuit optimization of optical fiber sensors. Such a fast simulation and the compensated optical circuit nearly acted as if a free space are unprecedented in open literature. The invention is briefly described as follows.